The lights on the unit (42151685767) are fine but my phone is still ignoring it after I switched to a new SIM.

I have de-registered and registered (leaving 24 hours between the two). According to my account the SS3 is now 'active'. I have rebooted my phone. Nothing has changed concerning my internet connection so I don't see that being the issue.

Yah, that did it. I suddenly guessed that after reading these two snippets of information:

From the SS3 FAQ:

"Will my Sure Signal work with 4G?

Your 4G signal is not boosted by your Sure Signal – but your 3G signal still is. So when you take a call, your device is automatically on 3G and uses your Sure Signal, as we don’t offer calls over 4G.

When using data on your device at home, our 4G signal takes priority over your Sure Signal if you’re not connected to your home Wi-Fi network."

and elsewhere:

"Experience crystal clear calls with HD Voice from Vodafone. This new technology improves the quality of each person’s voice while reducing background noise on every call between compatible Vodafone mobiles."

Maybe someone ought to update the FAQ. Since I don't want to limit my phone to 3G this suggests I might as well dump the SS3. I'll just have to hope that wifi calling kicks in although so far it shows no sign of doing so even when my phone is only showing one bar.

"After you have received a text that confirms wifi calling is now active..."

Because until you get that second text the Wifi Calling menu item will not be visible.

It's also worth pointing out that if you send the 'Calling' text too soon after SIM activation the first reply will come back but the service will never be activated. That's what happened to me. I sent the text, got the first reply then spent several hours swearing at Vodafone and wondering if I ought to give up and send the phone back. It was only in desperation that I sent the text again and within five minutes got the second response telling me wifi calling was active.

Frankly every time I have dealing with Vodafone it ends up like this. Poor documentation and frustration.